Molding is a common method used to manufacture a large variety of items. In many cases, a mold includes several pieces which must fit together in order to define the mold volume (i.e., the space to be filled with plastic or other material being molded into a manufactured part). In some cases, a single mold may actually include elements used to mold several parts. One example is a mold used to form outsoles for a pair of shoes. Such a mold is used to simultaneously mold the upper and lower surfaces of two outsoles—a right shoe outsole and a left shoe outsole. Conventional outsole molds can include two mold halves. The first mold half is used to mold the upper surfaces of a pair of outsoles. The second mold half mates with the first half, and is used to mold the lower surfaces of the outsole pair. Each mold half has traditionally been cast as a single piece of steel or other metal, and can be quite heavy.
The location of the parting line can be important when molding shoe outsoles. As is known in the art, the parting line is where portions of a mold meet and seal. Because the seal is often not perfect, a small amount of molded material will often seep through the parting line and leave “flash” on the molded part. Removing flash from a molded part requires extra labor and increases manufacturing cost. Even in the absence of flash, however, a molded part often has a noticeable ridge that corresponds to the parting line. For these reasons, it is advantageous to construct the mold so that the parting line is in a less noticeable location. For outsoles, this often means locating the parting line along an upper edge of the outsole. This upper edge sometimes follows a complex curve.
Beyond being heavy and cumbersome, conventional outsole molds can be expensive and time-consuming to fabricate. In particular, achieving a desired parting line often requires significant hand finishing work after the mold halves are cast. Because of the large amounts of metal used to cast conventional outsole molds, forming the parting line as part of the casting process is difficult. In particular, the large metal volume of a cast mold half holds substantial heat, and significant warpage can occur as the cast mold cools. In order to reduce this warpage, the size of the mold could be reduced by, e.g., separating the upper and lower halves into smaller separate left and right elements. However, this presents additional challenges. For example, joining multiple smaller elements together can introduce additional manufacturing steps into the mold making process.